Resin compositions for producing biaxially oriented polypropylene films

ABSTRACT

Polypropylene resin compositions are provided that are useful in the production of biaxially oriented polypropylene films (BOPPs). The resins of the present invention are blends of high crystalline (low solubles) polypropylene homopolymer and an ethylene/propylene random copolymer (RCP). These blends can be used to replace standard high solubles BOPP grade polypropylene homopolymers. In addition, the use of high crystalline polypropylene homopolymers in the blends imparts improved stiffness to the finished films while maintaining good processability of the blends.

FIELD OF THE INVENTION

[0001] The present invention is drawn generally to the field ofpolypropylene resins. More specifically, the present invention is drawnto the field of polypropylene resins for the manufacture of biaxiallyoriented polypropylene films.

BACKGROUND OF THE INVENTION

[0002] BOPP (biaxially oriented polypropylene) film is produced bydrawing a cast sheet of polypropylene in two directions at a temperaturebelow the melting temperature of the resin. Specific characteristics arerequired for the standard polypropylenes used to produce BOPP materials,such as relatively larger amounts of xylene solubles, and relatively lowisotacticity. It is known that for a given PP, the lower theisotacticity, the lower the melting temperature of the PP and the betterits processability to BOPP film. However, these same properties in thePP result in poorer properties of the resulting film. Therefore, thereexists a processability-property trade-off in BOPP materials. Inaddition, production of high solubles materials generally used for BOPPfilms is not easy because it requires a specific catalyst system andcareful handling of powder. It is known that it is difficult to producea homopolymer containing xylene solubles fractions higher than 6%because a specific catalyst system as well as careful handling ofpolymer powder in the reactor are required. In general, the largeamounts of xylene solubles in the polypropylene become sticky and oftencause agglomeration of polymer powder in the reactor, disruptingcontinuous production at the plant.

[0003] To avoid the problems of producing high solubles material, blendsthat improve the processability of low solubles material have beeninvestigated. It is well known that isotactic PP (iPP) produced by aZiegler-Natta (ZN) catalyst has a broad isotacticity and molecularweight distribution, thus exhibiting a broad melting temperature range.Conversely, PP produced by a metallocene catalyst exhibits narrowisotacticity and molecular weight distribution and thus, the meltingtemperature range is relatively narrow. Unlike PP produced by ZNcatalyst, some degree of regio-mis-insertion, i.e., “head-to-head” or“tail-to-tail” insertions, of monomer exists in the metalloceneisotactic PP (m-iPP). The melting temperature of m-iPP is also affectedby the degree of regio-mis-insertion in addition to isotacticity. Thus,an iPP of much lower melting temperature than conventional ZN-iPP can beproduced with a metallocene catalyst. When employed in BOPP film,however, a much narrower temperature window for drawing is available dueto the narrow tacticity and molecular weight distribution.

[0004] The effect of the addition of m-iPP to ZN-iPP on BOPP film wasexplored by Phillips et al, J. of Applied Polymer Science, 80, 2400(2001). It was found that the addition of m-iPP to ZN-iPP provides abalance of elevated temperature draw performance and room temperaturefilm properties relative to the ZN-iPP materials. Improvedprocessability of the BOPP film including fewer webs breaks anddrawability at higher line speeds have been claimed by the addition ofsome amounts of metallocene syndiotactic PP to ZN-iPP in U.S. Pat. No.6,207,093 to Hanyu, Mar.27, 2001, Fina Technology. The addition of someamounts of modifier tends to improve processability of iPP and/orproperties of the resulting film. The selection of the modifier dependson the desired film properties and availability of modifier.

[0005] In U.S. Pat. No. 5,691,043, to Keller et al addition of variousatactic and syndiotactic polypropylenes, as well as various propylenecopolymers to a standard BOPP grade isotactic polypropylene homopolymerto produce a core layer for multi-layer a uni-axially shrinkable film isdiscussed. However, Keller does not discuss the possibility of replacingstandard BOPP grade polypropylene homopolymers with low soluble contentmaterial.

[0006] In addition to seeking replacements for high solublespolypropylenes, BOPP film manufacturers have long sought a material thatprovides a stiffer oriented film while maintaining acceptablestretchability. High crystalline PP materials impart the desiredstiffness to the finished articles, however, these materials aregenerally not suitable for processing into BOPP films. This pooroperability of high crystalline materials is reported in U.S. Pat. No.5,691,043.

[0007] It would be desirable to provide a resin composition suitable forproducing BOPP films that has both good processability and imparts thedesired characteristics to the finished film. It would further bedesirable to provide a resin for producing BOPP films that avoids theproblems associated with producing high soluble content PP homopolymers.Such compositions could also comprise a high content of high crystallinepolypropylene homopolymer to impart greater stiffness to the material.

SUMMARY OF THE INVENTION

[0008] The present invention provides blends of non-BOPP gradepolypropylene homopolymers with ethylene/propylene random copolymers.The compositions comprise from about 70% to about 95% of a non-BOPPgrade polypropylene homopolymer and from about 5% to about 30% of anethylene/propylene random copolymer. The blends allow the use ofpolypropylene homopolymers having a higher crystallinity (lower solublescontent) than would otherwise be necessary for processing into BOPPfilms.

[0009] The compositions according to the current invention can beproduced either by melt blending of separate resin powders or by anin-situ in reactor blending process during production of the polymers.

BRIEF DESCRIPTION OF THE FIGURES

[0010]FIG. 1 shows the T.M. Long Yield Stress of various compounds as afunction of temperature.

[0011]FIG. 2 shows the T.M. Long yield stress stretched at 280 and 290°F. as a function of cast sheet density.

[0012]FIG. 3 shows the thermal fractionation endotherms of HCPP(FF050HC) and its blend with 30% RCP in comparison to FF029A (31J026).

[0013]FIG. 4 shows the T.M. Long Yield Stress of various compounds as afunction of temperature.

[0014]FIG. 5 shows the T.M. Long yield stress stretched at 280 and 290°F. as a function of cast sheet density.

[0015]FIG. 6 shows the Tensile Stress of films made from various resins.

[0016]FIG. 7 shows the Tensile Modulus of films made from variousresins.

[0017]FIG. 8 shows the Haze of films made from various resins.

[0018]FIG. 9 shows the % Transmittance of films made from variousresins.

[0019]FIG. 10 shows the 45 degree gloss of films made from variousresins.

[0020]FIG. 11 shows the Shrinkage of films made from various resins.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The resin compositions according to the current invention areblends of non-BOPP grade polypropylene homopolymers andethylene/propylene random copolymers. The blends according to thecurrent invention may be produced either by melt blending separatepowders or by producing the blend in-situ in an in reactor process. Ineither case, the blends according to the current invention displayprocessing characteristics that are comparable to or better thanstandard BOPP grade polypropylene homopolymers. Additionally, films madewith resins according to the current invention display improvedqualities in terms of haze, gloss and stiffness over films producedusing standard BOPP grade polypropylene homopolymers.

[0022] Films comprising the resins according to the current inventioncan be made by any commercial process for producing films comprisingstandard BOPP grade homopolymers. For example, two prevalent commercialprocesses for producing oriented films are the tenter frame process andthe “bubble” or blown film process.

[0023] In a typical tenter frame process, molten polymer is supplied toa flat slot die, from which a cast sheet or film is extruded. This castsheet or film is then conveyed to a chill roller where it is cooled to asuitable temperature. The cast sheet or film is then conveyed to apre-heat roller where it is heated to an appropriate stretchingtemperature. Stretching in the machine direction is accomplished bymeans of a pair of sequential rollers. The first, slow roller isfollowed by a second fast roller that rotates at a speed sufficient togenerate a surface speed that is typically 4-7 times faster than theslow roller. The speed differential between the fast and slow rollerscauses a 4-7 fold stretching of the cast sheet or film in the machinedirection. After stretching in the machine direction, the film is thencooled again by additional chill roller(s) before being conveyed to asecond pre-heat roller where it is heated to an appropriate temperaturefor stretching in the transverse direction. The transverse stretchingsection of the tenter frame then stretches the film by means of aplurality of tenter clips, which grasp the opposite sides of the filmand stretch it in a lateral direction. The concluding portion of thestretching process may include an annealing section. After chilling toan appropriate temperature“, the film is then trimmed of waste and thenapplied to take up spools.

[0024] The typical steps involved in the bubble or blown film processinclude extruding the molten polymer is through an annular die andquenching in water to form a calibrated tube. The tube is then conveyedto the orientation tower where it is reheated to the optimum temperaturefor orientation. At the top of the tower, the tube is squeezed airtightby the first stretching nip. The tube is then heated and inflated withhigh-pressure air to form a large diameter bubble. The bubble orientsthe film in the transverse direction while simultaneously, the bubble isstretched in the machine direction by the speed differential between thefirst and second stretching nips. The oriented bubble is then collapsedby converging rolls and then annealed. After annealing, the film is slitinto two webs. Each web is corona treated or flame treated and thenwound.

[0025] Those skilled in the art will recognize that these examples of atenter frame and bubble process are for illustrative purposes only.Variations on either process are within the knowledge of one skilled inthe art and are considered to be within the scope of the presentinvention. Further, films produced using the resin compositionsaccording to the current invention are not limited to those produced byeither the tenter frame or bubble process. The resin compositionsaccording to the current invention are useful in the production of BOPPfilms generally and are not limited to the specific methodologydisclosed herein.

[0026] The resin compositions according to the current inventioncomprise from about 70% to about 95% of a low solubles polypropylenehomopolymer and from about 5% to about 30% of an ethylene/propylenerandom copolymer. Preferably, the resin compositions according to thecurrent invention comprise from about 70% to about 85% of a low solublespolypropylene homopolymer and from about 15% to about 30% of anethylene/propylene random copolymer (RCP).

[0027] Polypropylene homopolymers that are suitable to be used in thecompositions according to the current invention have a crystallinecontent of at least 55%, and a solubles content less than about 3%,preferably less than about 2%. Examples include, but are not limited to:F020HC, F050HC from Sunoco, 3576X from AtoFina, 9433x from BPAmoco andNovolen 1040NX from Targor. The ethylene/propylene RCPs that aresuitable for use in the resin compositions according to the currentinvention contain from about 0.5% to about 7% of ethylene, preferablyabout 2.5% ethylene. Examples of ethylene/propylene copolymers include,but are not limited to: TR3020F, TR3005, TR3020SF from Sunoco, 8573 fromAtoFina, 8249 from BPAmoco and 256M from Basell.

[0028] The resin compositions according to the current invention can beproduced by melt blending a low solubles polypropylene homopolymer withan ethylene/propylene copolymer by compounding in a known way.Preferably, the resin compositions according to the current inventionare produced in-situ in a multi reactor process. For example, in a fourreactor process, the polypropylene homopolymer may be produced in thefirst two reactors. The ethylene/propylene RCP may then be produced inthe third and fourth reactors as the homopolymer continues topolymerize. Alternatively, in a two reactor process, the polypropylenehomopolymer is made in the first reactor and the ethylene/propylene RCPmay be made in the second reactor as the homopolymer continues topolymerize. In this way, the ethylene/propylene RCP may be distributedmore uniformly in the blend. Although production of the blends by an inreactor process is preferred, blends made by either method are suitablefor producing BOPP films according to the current invention.

[0029] The resin compositions and BOPP films according to the currentinvention may also include a number of additives, including but notlimited to: nucleators, anti-oxidants, acid neutralizers, slip agents,antiblock, antifogging agents and pigments.

EXAMPLE 1

[0030] Conventional Polypropylene

[0031] Several samples of a resin blend according to the currentinvention were prepared using a conventional non-BOPP gradepolypropylene homopolymer having low solubles. Polypropylenehomopolymer, D022D, available from Sunoco, was melt blended with variousamounts of a random copolymer resin having 2.5% ethylene, TR3020F,available from Sunoco. A commercial BOPP grade polypropylene, FF020D,available from Sunoco, containing relatively large amounts of xylenesolubles, e.g., 4.9%, was included for comparison. The various blendsprepared are shown in Table 1. TABLE 1 Compositions Prepared Resin A B CD E F D022 100 95 90 80 TR3020 5 10 20 100 FF020D 100

[0032] The characteristics of compounds containing random copolymeralong with homopolymers and random copolymer are given in Table 2. TABLE2 Characteristics of compounds containing RCP in comparison to FF020DProperty A B C D E F D022 100 95 90 80 TR3020 5 10 20 100 FF020D 100(30H036) MFR 2.0 1.8 1.8 1.8 2.4 2.0 % XS 2.9 2.9 3.1 3.3 5.2 4.9Mn/1000 64 64.9 65.0 65.7 65.9 66.0 Mw/1000 333 330 328 322 296 349Mz/1000 930 912 917 874 751 1045 D 5.22 5.08 5.05 4.91 4.49 5.29 D′ 2.792.76 2.80 2.71 2.54 — T_(m) (° C.) 164.8 164.8 163.1 162.9 149.2 — T_(c)(° C.) 115.0 112.5 112.1 112.0 103.4 — % X_(c) 58.7 57.3 57.5 56.3 45.653.9

[0033] It is known that the isotacticity of the insoluble fraction ofpolypropylene and the amounts of solubles are inversely related anddetermine the crystallinity of the polymer. Thus, a random copolymer(RCP) that has relatively lower crystallinity with larger amounts ofxylene solubles than a homopolymer could modify (or decrease) theoverall crystallinity when added to homopolymer. Table 2 indicates thatthe addition of RCP slightly increases the amounts of xylene solubles,decreases the overall crystallinity and the recrystallizationtemperature. Addition of 20% RCP was not, however, enough to decreasethe overall crystallinity of the compound to the same level as that ofthe standard BOPP grade polypropylene. Based on the additive rule, itappears that about 40% RCP is required to have a comparable overallcrystallinity to FF020D.

[0034] Cast Sheet and T.M. Long Films

[0035] Cast sheets 22-23 mil thick were prepared from these materials inTable 2 using HPM sheet line (L/D=30) under the conditions shown inTable 3. The extruder was equipped with a flat die for verticalextrusion. The polymer melt extruded through the die was quenched on toa chill roll into the sheet. The temperature of the chill roll was keptat 110° F. (43.3° C.). TABLE 3 Zone 1 2 3 4 Die 1 Die 2 Melt Temp. Temp.(° C.) 204 246 260 260 260 260 263

[0036] The density of the extruded sheets was measured in a TechneDensity column containing 558 ml H₂O and 322 ml isopropanol mixture inthe heavy flask and 327 ml H₂O an 553 ml isopropanol in the light flask.

[0037] For film preparation, polypropylene was extruded onto a cast rollto produce either 0.254 or 0.508 mm thick sheet. Samples (5.08 cm×5.08cm) were cut out of the sheet stock and stretched with a T. M. Longstretcher (T. M. Long Corporation, Somerville, N.J.). This equipmentallows simultaneous and/or consecutive biaxial orientation at anelevated temperature. Samples were stretched with the T.M. Long at agiven stretching temperature and a fixed strain rate of 50.8 mm/secafter 25 sec. pre-heating. The tensile biaxial stress-strain curve issimultaneously generated during orientation. The sheets were stretchedto 0.6-0.7 mil film by simultaneous stretching at 6.2×6.2 draw ratio.The film properties were determined by the method prescribed in ASTM882. Table 4 gives the density of the cast sheet, T.M. Long yield stressand film properties while FIGS. 1 and 2 show the dependence of T.M. Longyield stress on the stretching temperature and the cast sheet density,respectively. In accordance with the overall crystallinity of thecompound, the density of the cast sheet also decreases with increasingamounts of RCP. The T.M. Long yield stress decreases with increasingstretching temperature and/or with decreasing the density of the castsheet as shown in FIGS. 1 and 2. TABLE 4 Density of sheet stock and T.M.Long yield stress 667A 667B 667C 667D 667E 884A Resin Composition D0225% RCP 10% 20% TR3020 FF020D RCP RCP (30H036) Density (cast sheet)0.9028 0.9025 0.9017 0.9017 0.8957 0.8988 TML yield stress (psi) @ 138°C. 505 494 486 458 125 404 @ 143° C. 377 390 378 319 38 294 @ 149° C.258 251 234 199 — 174

[0038] It is noted that FF020D that has 4.9% xylene solubles exhibitsabout 100 psi lower T.M. Long yield stress than D022 that has 2.9%xylene solubles irrespective of the stretching temperature. TR3020 thathas 2.5% ethylene and 5.5% xylene solubles has significantly lower T.M.Long yield stress than FF020D. It can be attributed to the lower meltingtemperature and overall crystallinity of the random copolymer along withlarger amounts of xylene solubles than the homopolymer. These resultsindicate that the crystalline state at the stretching temperaturedictates the T.M. Long yield stress. It should be noted that thecrystalline state of a polypropylene at a stretching temperaturepredominantly affects the viscosity of the “pseudo-melt” (because thepolymer is partially melted) along with molecular weight. Table 5 givesthe properties of film produced with T.M. Long stretcher. These resultsindicate that the tensile properties and haze of the compounds arecomparable to those of homopolymer, i.e., FF020D, even at 20% additionof random copolymer. These results indicate that the homo-randompolypropylene can be employed as an alternative BOPP material replacinghigh solubles homopolymer. TABLE 5 Properties of film produced at 138°C. by stretching at 6.2 × 6.2 ratio 667A 667B 667C 667D 667E 884A ResinComposition D022 5% RCP 10% 20% TR3020 FF020D RCP RCP (30H036) TensileStress (kpsi) 27.1 31.4 31.1 30.3 21.9 27.1 Tensile Strain (%) 63.2 70.272.4 74 59.9 69 Modulus (kpsi) 367 370 370 254? 363 332 Haze 0.63 0.630.68 0.63 0.67 0.65

EXAMPLE 2

[0039] High Crystalline Polypropylene

[0040] A second set of compositions was prepared using a highcrystallinity polypropylene homopolymer, F050HC, available from Sunoco.The random copolymer, TR3005, available from Sunoco, having 2.5%ethylene, was melt blended with the HC homopolymer via compounding asgiven in Table 6. A conventional BOPP material, FF029A, available fromSunoco, designed for the core material of clear film, was used as acontrol. TABLE 6 Compounds prepared in this study 2100944 A B C D F050HC% 100 85 70 TR3005 % 15 30 FF029A (31J026) 100

[0041] The melting temperature and recrystallization temperature foreach composition was determined using annealed differential scanningcalorimetry (ADSC). The polymers were melted at 230° C. for 5 minutesand cooled to 0C at a rate of 10° C./min while recordingrecrystallization exotherm. Then, the sample was heated to 190° C. at arate of 10° C./min to record the melting endotherms.

[0042] The materials were also evaluated by thermal fractionation. Thepolymer melt was cooled to 170° C. at a rate of 20° C./min, followed byisothermal crystallization process during which the sample was held for4 hrs. The isothermal crystallization process continued to decrease to130° C. at 10° C. decrement. The temperature of the sample was thendecreased to 0° C., and the sample was analyzed as it was heated to 200°C. at a rate of 10° C./min. to record the melting endotherm. It has beendiscovered that how well a material stretches on a tenter frame dependson the shape of endotherm recorded from the thermal fractionation. Thus,the thermal behavior of the compositions produced were evaluated via thethermal fractionation method as shown in FIG. 3. As can be seen, theblend with 30% of RCP has a trace similar to that of the standard BOPPgrade material.

[0043] The characteristics of materials produced are given in Table 7.The commercial BOPP grade, FF029A that contains relatively large amountsof xylene solubles, e.g., 5.8%, was included for comparison. As noted inthe previous Example (1), a RCP that has 2.5% ethylene has relativelylower crystallinity and larger amounts of xylene solubles than ahomopolymer. Therefore, when added to homopolymer, a RCP should modify,i.e., decrease, the overall crystallinity. Table 7 confirms that theaddition of RCP to a homopolymer slightly increases the amounts ofxylene solubles, decreases the overall crystallinity and therecrystallization temperature. It is noted that the blend of F050HC with30% TR3005 has a slightly higher crystallinity than FF029A. Themolecular weight and distributions of all the polymers are comparablewithin the limit of experimental error. TABLE 7 Characteristics ofcompounds containing RCP in comparison to FF029A A B C D 2100944 F050HC15% TR3005 30% TR3005 FF029A (31J026) MFR 6.2 4.6 3.7 3.0 % XS 1.73 2.283.12 5.82 T_(m)(° C.) 163.7 162.2 159.3 159.1 T_(c)(° C.) 118.1 115.1112.9 112.6 % X_(c) 61.9 58.6 55.2 53.3 Mn/1000 53.5 63.2 65.8 50.4Mw/1000 252 278 283 257 Mz/1000 779 819 838 988 D 4.7 4.4 4.3 5.1 D′ 3.12.9 3.0 3.8

[0044] DHOT

[0045] Cast Sheets and T.M. Long Films

[0046] As in Example 1, cast sheets 22-23 mil thick sheet were producedusing HPM sheet line (L/D=30) under the conditions in Table 8. TABLE 8Zone 1 2 3 4 Die 1 Die 2 Melt Temp. Temp. (° C.) 204 246 260 260 260 260263

[0047] The temperature of the chill roll was kept at 110° F. (43.3° C.).The density of the extruded sheets was measured in a Techne Densitycolumn containing 558 ml H₂O and 322 ml isopropanol mixture in a heavyflask and 327 ml H₂Oan 553 ml isopropanol in a light flask.

[0048] The 22-23 mil sheets were stretched to 0.6-0.7 mil film bysimultaneous stretching at 6.2×6.2 draw ratio with T.M. Long after 25sec. pre-heating at a given stretching temperature. The yield stress wasmeasured while stretching the cast sheet.

[0049] The film tensile properties were determined by the methodprescribed in ASTM 882.

[0050] Strips (1″×8″) from T.M. Long film were used to determine thetensile properties. Although ASTM recommends 10″ grip separation and 1in/min crosshead speed for the measurement of tensile modulus, 4″ gripseparation was employed due to the size of the T.M. Long film.Accordingly, the crosshead speed was adjusted to 0.4 in/min. For allother tensile properties, the crosshead speed was 2 in/min. At least 5specimens were tested.

[0051] Optical properties such as transparency, haze and clarity of thefilm were evaluated by the method prescribed in ASTM 1003 (Haze and %transmittance) and ASTM 1746 (clarity).

[0052] Gloss was measured at the 3 different angles, 20, 45 and 60degree by using the method described in ASTM 2457, where 60-deg. isrecommended for intermediate gloss films, 20-deg. for high gloss filmsand 45-deg. for intermediate and low gloss films.

[0053] Shrinkage was measured using ASTM D2732. A rectangular cutout(3.9″×3.9″) from the T.M. Long film was placed in a “Free Shrink” holdersuch that the cutout is free from contact with the edge of the holder.Then, the holder was immersed in an oil bath for at least 10 seconds ata given temperature in order for the material to come to thermalequilibrium and undergo maximum shrinkage. The holder was removed fromthe oil bath and quickly immersed in oil at room temperature. After atleast 5 seconds, the sample was removed from the oil. After removing theremaining oil from the specimen, the dimension of the specimen wasmeasured and the shrinkage was calculated using the equation:

% shrinkage=(L _(o) −L _(f))/L _(o)×100

[0054] where L_(o) is the initial length and L_(f) length aftershrinking.

[0055] Table 9 gives the density of the cast sheet, the T.M. Long yieldstress and film properties while FIGS. 4 and 5 show the dependence ofthe T.M. Long yield stress on the stretching temperature and the castsheet density, respectively. TABLE 9 Density of sheet stock and T.M.Long yield stress A B C D Resin F050HC 15% TR3005 30% TR3005 FF029AComposition Density     0.9043 0.9034 0.9026 0.9029 (Cast Sheet) T.M.Long yield stress @ 138° C.   779^(a) 644 549 519 @ 143° C. 594 496 418390 @ 149° C. 445 365 281 253

[0056] In accordance with the overall crystallinity of the materials,the density of the cast sheet decreases with increasing amounts of RCPas does the T.M. Long yield stress as shown in FIGS. 4 and 5. While theT.M. Long film of FF050HC tore after yielding when stretched at 138° C.,the blend containing 15% random copolymer did not tear when stretched.It is noted that although the blend that contains 30% random copolymerhas a slightly lower density than FF029A, its T.M. Long yield stress ishigher as shown in FIG. 5. Since the T.M. Long yield stress depends onthe density, i.e., crystallinity, of the cast sheet at the stretchingtemperature, it appears that the blend containing 30% random copolymershould have a higher density at the stretching temperature than FF029Adoes.

[0057] The properties of film produced at 3 different temperatures witha T.M. Long stretcher are given in Table 10 and depicted in FIGS. 6-11.The results in Table 10 may be summarized as follows. The T.M. Longfilms produced from the blends exhibit higher tensile properties thanthose produced from FF029A. Haze and % transmittance of the filmproduced from the blends at 138° C. and/or 143° C. are comparable tothose produced from FF029A. However, when stretched at 149° C., the filmproduced from FF029A is much hazier than those from the blends. The45-degree gloss varies depending upon the stretching temperature. Theshrinkage of the film from the blends is slightly lesser than that fromFF029A. TABLE 10 Properties of T.M. Long film produced at varioustemperatures A B C D 2100944 F050HC^(a) 15% TR3005 30% TR3005 FF029A138° C. Haze — 0.90 0.58 0.63 Transmittance (%) 94.5 94.4 94.5 Clarity —97.4 98.1 98.0 Gloss 20 — 36.1 27.2 41.0 45 — 93.1 90.3 93.7 60 — 129.7114.2 114.2 Tensile stress (kpsi) — 31.6 32.4 33.4 Tensile strain (%) —68.6 70.0 72.0 Modulus (kpsi) — 524 471 448 Shrinkage (%) — 17.5 19.919.5 143° C. Haze — 0.72 0.77 0.61 Transmittance (%) — 91.9 92.6 92.2Clarity — 97.8 97.4 98.9 Gloss 20 — 47.1 89.4 84.3 45 — 86.2 86.2 91.760 — 127.2 126.3 126.4 Tensile stress (kpsi) 33.4 35.6 33.4 32.3 Tensilestrain (%) 75.0 77.3 80.0 72.1 Modulus (kpsi) 601 579 561 496 Shrinkage(%) — 16.16 19.65 18.17 149° C. Haze 1.58 2.63 2.5 6.08 Transmittance(%) 91.2 90.9 91.1 87.2 Clarity 95.3 90.5 91.3 87.1 Gloss 20 44.5 67.147.3 46.7 45 88.9 85.8 86.3 79.3 60 113.9 114.4 109.1 103.8 Tensilestress (kpsi) 29.5 27.2 29 24.7 Tensile strain (%) 83.6 65 81.5 66Modulus (kpsi) 536 470 521 356 Shrinkage (%) 8.3 10.1 9.1 10.1

[0058] The examples provided demonstrate that the addition of RCP to ahomopolymer, which has relatively small amounts of xylene solubles andis not easily stretchable, facilitates the stretchability of thehomopolymer. Thus it is possible to replace standard high solubles BOPPgrade polypropylene homopolymers with lower solubles content materials.This is especially advantageous to produce a stiffer film since a highcrystalline PP can be modified to be stretchable under the conventionalprocessing conditions. Further, the films produced from the blendcontaining RCP exhibit improved properties over films produced withstandard BOPP grade polypropylene.

[0059] The present invention has thus been described in general termswith reference to specific examples. Those skilled in the art willrecognize that the invention is not limited to the specific embodimentsdisclosed in the examples. Those skilled in the art will understand thefull scope of the invention from the appended claims.

What is claimed is:
 1. A resin composition suitable for processing intoa biaxially oriented polypropylene film, the composition comprising:about 70% to about 95% by weight of a polypropylene homopolymer, saidpolypropylene homopolymer having less than 3% by weight xylene solubles;and about 5% to about 30% by weight of an ethylene/propylene copolymer,said ethylene/propylene copolymer containing from about 0.5% to about7.0% ethylene by weight.
 2. The resin composition according to claim 1,wherein said polypropylene homopolymer has a crystallinity of at least55%.
 3. The resin according to claim 1, wherein said resin is producedby in reactor blending.
 4. The resin composition according to claim 1,further comprising at least one additive selected from the groupconsisting of: nucleators, anti-oxidants, acid neutralizers, slipagents, antiblock, antifogging agents and pigments.
 5. The resincomposition according to claim 1, wherein said composition comprisesabout 70% to about 85% of a polypropylene homopolymer having less than3% by weight xylene solubles, and about 15% to about 30% by weight of anethylene/propylene copolymer, said ethylene/propylene copolymercontaining from about 0.5% to about 7.0% ethylene by weight.
 6. Abiaxially oriented polypropylene film comprising: about 70% to about 95%by weight of a polypropylene homopolymer, said polypropylene homopolymerhaving less than 3% by weight xylene solubles; and about 5% to about 30%by weight of an ethylene/propylene copolymer, said ethylene/propylenecopolymer containing from about 0.5% to about 7% ethylene by weight. 7.The biaxially oriented polypropylene film according to claim 6, whereinsaid polypropylene homopolymer has a crystallinity of at least 55%. 8.The biaxially oriented polypropylene film according to claim 6, furthercomprising at least one additive selected from the group consisting of:nucleators, anti-oxidants, acid neutralizers, slip agents, antiblock,antifogging agents and pigments.
 9. The biaxially oriented polypropylenefilm according to claim 6, wherein said composition comprises about 70%to about 85% of a polypropylene homopolymer having less than 3% byweight xylene solubles, and about 15% to about 30% by weight of anethylene/propylene copolymer, said ethylene/propylene copolymercontaining from about 0.5% to about 7.0% ethylene by weight.
 10. Amethod of producing a biaxially oriented polypropylene film, the methodcomprising: providing a resin composition comprising: about 70% to about95% by weight of a polypropylene homopolymer, said polypropylenehomopolymer having less than about 3% by weight xylene solubles, andabout 5% to about 30% by weight of an ethylene/propylene copolymer, saidethylene/propylene copolymer containing from about 0.5% to about 7%ethylene by weight; extruding said resin composition into a cast sheet;and stretching said cast sheet in a first machine direction, andstretching said cast sheet in a second transverse direction, to producea biaxially oriented film.
 11. The method according to claim 10, whereinsaid stretching in a first machine direction and said stretching in asecond transverse direction are performed simultaneously.
 12. The methodaccording to claim 10, wherein said stretching in a first machinedirection and said stretching in a second transverse direction areperformed consecutively.
 13. The method according to claim 12, whereinsaid stretching is performed on a tenter frame apparatus.
 14. The methodaccording to claim 13, wherein said stretching in said first machinedirection is performed at a temperature of from about 60° C. to about140° C. and said stretching in said second transverse direction isperformed at a temperature from about 130° C. to about 170° C.
 15. Themethod according to claim 10, wherein said resin composition furthercomprises at least one additive selected from the group consisting of:nucleators, anti-oxidants, acid neutralizers, slip agents, antiblock,antifogging agents and pigments.
 16. The method according to claim 10,wherein said resin composition comprises about 70% to about 85% of apolypropylene homopolymer having less than 3% by weight xylene solubles,and about 15% to about 30% by weight of an ethylene/propylene copolymer,said ethylene/propylene copolymer containing from about 0.5% to about7.0% ethylene by weight.
 17. A method of producing a biaxially orientedpolypropylene film, the method comprising: providing a resin compositioncomprising: about 70% to about 95% by weight of a polypropylenehomopolymer, said polypropylene homopolymer having less than about 3% byweight xylene solubles, and about 5% to about 30% by weight of anethylene/propylene copolymer, said ethylene/propylene copolymercontaining from about 0.5% to about 7% ethylene by weight; extrudingsaid resin composition into a tube; and stretching said tube in a firstmachine direction, and inflating said tube with a gas to stretch saidtube in a second transverse direction, to produce a biaxially orientedfilm.